1. Field of the Invention
The present invention relates to a backlight module employed in a liquid crystal display device, and particularly to a backlight module having brightness enhancing structures configured for high and uniform brightness.
2. Description of Related Art
Because a liquid crystal display (LCD) device has the merits of being thin, light in weight, and drivable by a low voltage, it is extensively employed in various electronic devices.
A liquid crystal panel of an LCD device cannot itself emit light beams. Therefore a typical liquid crystal panel uses a backlight module to provide the needed illumination. The backlight module has a light source and a light guide plate. The light source emits the light beams to the light guide plate, which then transmits the light beams to illuminate the liquid crystal panel.
The light source may be a linear light source, or one or more point light sources. The light guide plate has an end face through which light is introduced, and two opposite major faces one of which functions as an emission face. The performance of the surface light source greatly depends on the characteristics of the light guide plate employed therein.
A light guide plate functions to change a direction of propagation of light beams emitted from the light source and introduced into the light guide plate, from a direction roughly parallel to the emission face of the light guide plate to a direction perpendicular to the emission face. That is, the light guide plate effectively changes the linear or point light source(s) into a surface light source, for evenly illuminating a whole display screen of the liquid crystal panel.
FIG. 10 shows a conventional backlight system 100, which has a light guide plate 103, a linear light source 101 adjacent the light guide plate 103, a reflector 104, and a brightness enhancing film 105 having a plurality of V-shaped prisms 1051. The reflector 104, the light guide plate 103 and the brightness enhancing film 105 are stacked in that order from bottom to top. The light guide plate 103 has a uniform thickness, and comprises an incident surface 1031, an emitting surface 1033, and a bottom surface 1032 opposite to the emitting surface 1033. A plurality of scattering dots 1034 is formed on the bottom surface 1032. The linear light source 101 is covered by a light source cover 102 on three sides thereof, for reflecting light beams into the light guide plate 103. The linear light source 101 is positioned adjacent the incident surface 1031 of the light guide plate 103, and emits light beams into the light guide plate 103 through the incident surface 1031. A proportion of the light beams thus introduced into the light guide plate 103 are reflected to the brightness enhancing film 105 by the bottom surface 1032. The brightness enhancing film 105 converges the light beams and introduces the converged light beams into an LCD (not shown). The backlight system 100 employs a plurality of optical elements and has a plurality of optical interfaces. The various optical interfaces cumulatively contribute to an unduly high loss of light intensity in the backlight system 100. That is, the backlight system 100 does not attain very effective optical utilization. Moreover, the brightness enhancing film 105 is generally expensive, and inflates the cost of the backlight system 100 proportionately.
It is desired to provide a new light guide plate and a corresponding backlight module which overcome the above-described problems.